Plecoptera 7 



KEY TO THE GENERA OF STONEFLIES (PLECOPTERA)* 



1 — With gills on a number of segments of the abdomen 2 



— With no gills (except anal gills) on the abdomen 4 



2 — With large single lateral gills on abdominal segments 1 to 7 Oroperla 



— With small tufted ventral gills on the basal segments only 3 



3 — These gills on segments 1 and 2 only Pteronarcys 



— These giUs on segments 1, 2 and 3 Pteronarcella 



4 — Body depressed, roach-like in form; head bent under Peltoperia 



— Body elongate, head directed forward 5 



5 — First and second tarsal segments very short, together less than half as long as the 



third segment 6 



— First and second segments more than half as long as the third 19 



6 — With 2 ocelli: copious gill tufts under the thorax 7 



— With 3 ocelli : gill tufts various or wanting 8 



7 — Ocelli close together; anal gills present Neoperla 



— Ocelli far apart (several diameters of one of them) Atoperla 



8 — With branched giU tufts at the base of the legs 9 



— With giUs if present minute unbranched and inconspicuous 12 



9 — Eyes set far forward, before the middle of the head Perlinella 



— Eyes not before the middle of the head 10 



10 — Body freckled with small brown dots: length 10 mm Perlesta 



— Body not so freckled ; size much larger 11 



11 — With distinct occipital ridge, continuous across the head Perla 



— Generally with this ridge not continued across the middle Acroneuria 



12 — With minute fingerlike gills at the throat 13 



—Without gills 14 



13 — These gills very minute (fig, 15) Hydroperla 



— These gills larger, and generally more numerous Perlodes 



14 — Head squarish with the small eyes set far forward 15 



— Head more convex at sides with the eyes more prominent laterally 16 



15 — Pronotal disc heavily fringed with coarse hairs: tails 8 mm Kathroperla 



— Pronotal disc not heavily fringed : tails 6 mm. long Paraperla 



16 — Outer margin of wing buds when grown incurving only at the ends: tails longer than 



either abdomen or antennee 17 



— Outer margin of wing buds broadly and regularly rounded: tails shorter than either 

 abdomen or antennae 18 



17 — Maxillae very large, their projecting "elbows" visible from above the head. .Isogenus 

 — Maxillae not visible from above the head Isoperla 



18 — Dorsum of thorax bare except for a few long hairs Chloroperla 



— Dorsum clothed with short scurfy pubescence Alloperla 



19 — Second tarsal segment as long as the first Taeniopteryx 



— Second tarsal segment shorter than the first 20 



20 — Hind wing cases much more widely divergent than the fore Nemoura 



— Hind wing cases parallel with those of the fore wings 21 



21 — Pale and slender: middle abdominal segments longer than wide Leuctra 



— Dark colored : middle abdominal segments wider than long Capnia 



* A standard reference work for this order is Claassen's Plecoptera Nymphs of North America, issued by the 

 Thomas Say Foundation, Dr. J. J. Davis, treasurer, Lafayette, Indiana (price S4.00). One for adult stoneflies 

 is Needham and Claassen's The Plecoptera oj North America, obtainable from the same source (price S5.00) 

 Prison's Plecoptera of Illinois (111. Nat. Hist. Survey 20: 281-471, 1935) treats more fully both nymphs and 

 adults of a more limited area. 



